1. Technical Field
The embodiments described herein relate to the field of video processing and more particularly to techniques on teletext information processing.
2. Description of the Related Art
Signals transmitted to television sets and many other display devices to generate displays typically include a vertical blanking interval (VBI). The VBI is the time between the last line of a frame and the beginning of the next frame. Often a portion of the VBI is used by television broadcasters to transmit control information necessary for displaying video information. This control information includes, for example, video synchronization signals. In addition, a portion of the VBI is typically reserved for broadcasting the text for closed captioning for the hearing impaired. Broadcasters also may use time within the VBI to broadcast a variety of other types of data, typically referred to as teletext, of the broadcaster's own choosing.
Teletext consists of information such as news, sports, and financial information. For instance, teletext broadcasts the latest stock prices, also recipes, entertainment listings, advertisements, movie schedules and reviews, music and TV program reviews, additional information on various TV programs, and more. Teletext also broadcasts subtitles (closed captions) for various programs, and news bulletins that are overlaid on top of the TV picture.
The total number of the frame lines is 525 for the National Television Standards Committee (NTSC) standard and 625 for Phase Alternating Line (PAL) standard. The line numbers of the teletext lines, for example, are set to be 5-22 or 317-334 alternated with the fields for the PAL standard (the line number is from 0 to 624), and 8-25 or 270-287 alternated with the fields for the NTSC standard (the line number is from 0-524).
FIG. 1 is a block diagram of a conventional video signal processing device 100 such as a conventional television set for receiving a television signal ‘STV’ and converting it for display. The television signal ‘STV’ comprises teletext information and video information. The teletext information and the video information are associated with a plurality of teletext lines and a plurality of video lines among a plurality of frame lines, respectively. Each teletext line comprises line enable signal ‘LES’ and teletext line data. Specifically, the line enable signal ‘LES’ records whether the teletext line is enabled or disabled and the teletext line data records a display data value of the teletext line. On the other hand, each video line comprises video line data. And specifically, the video line data records respective display data values associated with the video lines.
A receiver 110 receives the television signal ‘STV’, demodulates it into a transport stream ‘TS’, and then provides the transport stream to an extractor 120. The extractor 120, typically implemented as software, extracts the line enable signal ‘LES’ and line data information associated with all the frame lines from the transport stream TS. The extractor 120 then sends the line enable signal ‘LES’ to a plurality of registers 142 inside a VBI controller 140, wherein each of the registers 142 is dedicated to store the line enable signal ‘LES’ associated with a respective one of the teletext lines. Also, the extractor 120 provides line data ‘LD’ to a memory 130. The line data ‘LD’ comprises the teletext line data associated with the teletext lines (teletext line data ‘LD_TT’) and the video line data associated with the video lines (video line data ‘LD_VIDEO’).
The VBI controller 140 then reads the line enable signal ‘LES’ stored in the registers 140 to detect which teletext line is enabled. The VBI controller 140 reads from the memory 130 enabled teletext line data ‘LD_TTE’ associated with enabled teletext lines of the teletext lines and provides it to a TV encoder 160. A video controller 150 reads the video line data ‘LD_VIDEO’ associated with all of the video lines from the memory 130 and also provides it to the TV encoder 160. The TV encoder 160 then encodes the received line data ‘LD_TTE’ and ‘LD_VIDEO’ and provides the encoded data to the display 170 for display.
The total number of registers 142 is equal to that of the number of teletext lines. As high as 36 registers are required in the PAL or NTSC standard. Manipulation of such a great total number of the registers 142 causes the VBI controller 140 to have a heavy load and hence a large latency, especially during field transitions. Moreover, the fixed/disposed registers 142 restrict not only the total number but also the respective numbers of the teletext lines that can be used for teletext information transmission (e.g., always 5-22 or 317-334 for the PAL standard). Accordingly this leads to low information transmission flexibility, and adaptability.